Process of producing silicon steel



V. W. CARPENTER ET AL PROCESS OF PRODUCING SILICON STEEL June 23, 1942.

Filed Jan. 3, 1940 2 Sheets-Sheet l Effect of Dew Porn` of Hfdrogen on Decarburzafmr-a.l Open Annzaled IOOQF. for 5 Minutes.

TEMPERATURE `F Y INVENTORS.

Mero/ h( CARENTE/, HN /H/v M Zac/(son.

ATTORNEYS.

v. w. CARPENTER ETAL PROCESS PRODUCING SILICON STEEL Filed Jan. 3, 1940 2 Sheets-Sheet 2 Flnal Carbn O1 e'mp. 1500F.

\ Tem 1506*@ InniiiaiPCnrbovn .05

INVENTORS.

c7-OQ W CARPENTER,

A TTORNEYS.

Patented June 23, 1942 PROCESS F I RODUGING SILICON STEEL Victor W. Carpenter, Middletown, and John M. Jackson, Franklin, Ohio, assignors to The American Rolling Mill Company, Middletown,

Ohio, a corporation of Ohio `application January a, 1940, serial No. 31am 12 Claims.

Our invention relates to decarburlzation, and though not limited thereto, finds a. large field of utility in the production of silicon steel for magnetic purposes, which silicon steel is low in carbon; and we shall describe it principally in connection therewith.

It has long been ascertained that low carbon silicon steel has very many advantages .for mag- `netic uses; but there are a number of manufacturing difiiculties connected with the securing' of low carbon contents in materials of this class. Theoreticallythere should be three methods of securing silicon steel sheet or strip containing a minimum of carbon: First, if low carbon silicon steel ingots are made by special melting practice such as induction furnace melting, it should not be necessary to apply to silicon steel sheet or strip either in finished Iform or in the process of manufacture any treatment for the reduction of carbon. While it is possible to manufacture low carbon silicon steel ingots, and although .practices in this connection will likely be improved, yet at the present time it is difficult to get carbon values as low as 0.015 per cent-even in 'small experimental furnaces, and the application of such methods to the large scale, economical production of Isilicon steel has not yet been accomplished. Second, it is possible to give an intermediate treatment to silicon steel materials in the course of their manufacture into sheet or strip. As rset forth in the copending applications of Victor W. Carpenter Serial No. 60,347, filed January 22, 1936, and Serial No. 106,372,- flled October 19, 1936, it is a regular commercial practice with certain grades of silicon steelto hot roll'to an intermediate gauge and then box anneal the coiled hot-rolled material with theyhot mill scale on it at a temperature of between 1350 degrees and 1450 degrees F., substantially cold rolling the material and giving it the necessary heat treatments for magnetic properties. Third, it should theoretically be possible to box anneal the finished sheets in dry hydrogen and secure satisfactory decarburization. Y

It will be evident that where cold rolling is relied upon to reduce the material to final gauge, it will not be possible to follow a procedure analogous to the second mentioned method but carried on upon the intermediate or finished sheets, because of the absence of the mill scale or any equivalent decarburizing medium. So far as we are aware, prior to the work set forth 'in this application attempts to decarburize nished coldrolled silicon steel sheet or strip have not progressed beyond the experimental stage. AIt is possible to reduce carbon in silicon steelas low as 0.004 to 0.008 per cent by laboratory box annealing at around 2200.F. for many hours, in dry hydrogen. where the material is in narrow widths,

' say one or two inches; but as yet we have found `no cycle4 for commercial material which consistently gives low carbon values in the middle portion of wide widths, say sheets or strips to 36 inches'wide, other than the process ofthe present invention.

It may be set forth, therefore, as a fundamenl tal object of this invention that we provide a method of successfully and uniformly decarburizing silicon steel sheet or strip in commercial widths at intermediate or f'lnal gages without the necessity of the presence of oxide scale. By theA term decarburization as hereinafter employed, we mean a substantial per cent reduction of the carbon contentl to a final value which will depend on the desired properties of the final product and which Willalways be below 0.015% and often as low as 0.008% or less. This,'it will be understood, often amounts to a very considerable decrease in carbon content since the' most common commercial melting practices secure sillcon steels having carbon contents around 0.04 to 0.06%. f It is to be understood, however, that our new process is effective on silicon steels of lower carbon contents and we have, for example, successfully decarburized 0.02% carbon material to a nal value of 0.006%'.

But it is a further object of our invention to simplify, ycheapen and cut down the time duray tion of a decarburizing treatment carried on on finished sheets orstrips. In particular, in the practice of our invention we are able to decarburize these materials during a simple heat treatment of a very few minutes duration and of a character known'as open annealing. As aconsequence, itis a further object of our invention to provide a decarburizing treatment in the nature of an open anneal, preferably, though not necessarily, continuous, and to provide certain processes of producing silicon steel sheet or strip of very low carbon-content and good magnetic properties, whichV processes do not involve a box anneal, i

A further object of our invention is to provide an inexpensive and reliable method of decarburizs ing cold-rolled material at intermediate or flnal gages to such an extent that excellent magnetic a rapid and practical method of decarburlzing relatively narrow strips or sheets or punchings during a batch anneal in piles or coils `in which the width of the material is not vso great `as to prevent the effective access of the annealing atmosphere. l

In the preferred practice of our invention we have found that when we operate under certain conditions'hereinafter set'forth, and heat treat the material in awet reducing atmosphere we are able to attain the objects of Vour invention. By way of example in a certain procedure We reduce the carbon content of a silicon steel fromy its original value of say around 0.04 per cent to not more than 0.008 per cent within three minutes by open annealing the material in wet hydrogen, providing the proper conditions are set up.

The objects of our invention which have been A pointed out hereinabove or will be apparent to one skilled in the art upon reading these specifications, we accomplish by that certain procedure of which we shall now describe certain exemplary embodiments with the conditions surrounding them. i l 1 Reference is made to the drawings wherein we have charted the variable conditions susceptible of such a showing in the case where the reducing gas is Wet hydrogen, and wherein:

Figure 1 is a graph showing the effectl of the dew point of the hydrogen used in the open annealv on three classes of materials where the conditionsof temperature, time and gauge remain the same.

Fig. 2 is a graph for the same materials show-- f ture, dew point and gauge remain the same.

Fig. 4 is a solid diagram in which temperature, gauge and final carbon content are plotted against'eachother, the dew point remaining constant at around 130 F. (15 percent watervapor by volume) Fig. 5 is a solid diagram in which initial car-r bon, final carbon and the annealing temperature are plotted against each other, the dew point remaining constant at around130 F. (15 per cent water vaporby volume).

Fig. 6 is a solid diagram in which initial carbon, gauge and time are plotted against each other, the dew point remaining constant at around 130 volume). f f

Fig. 7l is a solid diagram in which final carbon, gauge and time are plotted against each other, the dew point remaining constant at around 130 F. (15 per cent water vapor by volume).

Invthe diagrams which form the drawings of this specification legends have been employed so that index numerals are not used. By initial carbon is meant the carbon content of the silicon steel sheet or strip material prior to the decarburizing treatment, while final carbon refers to its content after that treatment.

These diagrams were chosen as exemplary and have to do with the specific determination which form Figs. 1 to 3 inclusive; biit they are not limitations upon our invention,- our invention being applicable as hereinafter indicated, to all commercial gradesof silicon steel containing up-to approximately 4 per cent silicon. They are to be regarded primarily as illustrations of how the F. (15 per cent water vapor by decarburizat volves an open annealing in wet reducing gas such as hydrogen of a certain dew point, for a certain time and at a certain temperature. We shall now proceed to a discussionof'the various factors involved. As has been'pointed out, pure, dry hydrogen is an exceedingly slow and uncommercial decarburizing medium at any feasible temperature. Wet hydrogen is effective and rapid as we shall hereinafter more fully point out; but we believe that the active decarburizer in our preferred medium is the moisture content, and that the primary function fof the reducing gas is to prevent oxidation. For example, we have found that an atmosphere of steam will decarburize quite rapidly; but the'tendency to produce oxidation -of the sheet somewhat limits its utility as willV be understood. A reducing gas permits the decarburizing action but prevents oxidation. We have found in corrobora'tion of this' that the optimum of reducinggas will vary with its composition, with the moisture content, and with the temperature. From a metallurgical standpoint it would be desirable to use an atmosphere'containing nothing but hydrogen and water vapor; but from an economical vstandpoint it is frequently desirable to replace part of the hydrogen with nitrogen as occursA when dissociated ammonia is used; or'it may be desirable to use as a reducing atmosphere such gases as are commonly produced by thecontrolled combustion of natural gas. There is, as a consequence, a large permissible variation-of the composition'of the reducing gas of our preferred atmosphere; and this variation will be dictated by commercial expediency.' For best decarburization, however, atmospheres containing high percentages of -carbon bearing gases should be avoided.

The mechanism byV which 'carbon vis removed from the sheet or Istrip material is not known. A possible explanation is that either atomic oxygen or atomic hydrogen, or both, derived from the water vapor lis responsible for the rapid rate of ion, -While we do not desire to be bound by theory, our present feeling is that the water vapor decomposes at the surface of the sheet or strip under the temperature conditions vwhich are maintained and that there ensues a preferential oxidation of the s lcarbon in the presence of both iron-and silicon. l

The percentage ofnwater vapor in the atmosphere has a very importantr part inthe process of decarburization. At lowv percentages, for example, one per cent by' volume, the rate of carbon removal is very slow; but when the reducing atmosphere contains four per cent or more of water vapor the `rate of decarburization becomes quite rapid. This is illustrated in Fig. 1v for certain exemplary'analyses of material in an atmosphere of wet hydrogen. Moreover, as the percent of water vapor is increased therebeyond, the'rate of decarburization increases, but not as rapidly. lt will be noted from Fig. 1 that at 15 per cent of water vapor in the hydrogen the rate of decarburization is still increasing slowly; but it variables are related so that a skilled worker mosphere employed. VThe concentration of water .carburizatlon Thus iron and mild steels in genvapor which will cause scalingV willvary with the temperature', the material and the kcomposition of the balance of the atmosphere 'in a manner well within theV capability of th'ose skilled in the art to determine in the light of these teachings. For example, inV an atmosphere composed essentially of hydrogen at 1600 F., it should be permissible to use up to 35% water vapor by volume without scaling most ,steelsA 'For rapid decarburization water vapor contents should not be used which are below substantially 2`per cent by volume.

The best decarburizing temperatures for corny mercial open annealingywe have found lie approximately between 1400 andv 1600 F` As shown in'Figs. 4 and 5 the'decarbu'rization in a 'givenr time is substantially7 smaller both above and below this range. While very 'good results are obtained anywhere within this range on commercialV silicon grades, the optimum in decarburizationA willvary somewhat 'with the -silicon content yof the material as hereinafter described. The decarburization the ranges between 1350 and 14oo F. and between 1600 and 165o FL is alsovr substantial and will be satisfactory for some applications.

In the batchl annealing in wet' hydrogen of'l stacks or coils of relatively narrow material, ternperatures stilllower than 1350 F. andeve'n as" low as l200 F. will produce effective decarburization although the annealing time will havev to be somewhat lengthened. In this 'type of annelal, however, a decarburizing period of ra'iew hours or more is not commercially objectionable.

The time required for decarburization will depend to la considerable degree upon the gauge of the material used. Three minutes was found to be sufcient all other conditions being proper) when the'material was 0.014l inch thick; From the slope of the curve's'in Fig. 3 it Will be clear l' that,"al1.other conditions remaining the saine, it would require an anneal of approximatelyk `lei minutes to reduce the carbon in a material 0.025

eral may readilyV be decarburized by this method ifl a smallnpercentage of silicon is included in their analyses; and this makes possible the com- 'mercial production of very low carbon vmaterials of classes usually not included in the term elec-` trical steels, or silicon'steels where the term kis used to imply materials or relatively higher silicon contents intended primarily fory magnetic uses. Therefore where herein and in the claims which follow, we refer to silicon steel without other qualification, we ydesire to be understood as..

including also'ferrous materials containing sufiicient silicon for commercial dec'arburization by our'rnethod but below the silicon content ordinarily impliedl'by the termfsillcon steel.` Speciiically we desire to'be' understood as including ferrous;materialsinv which only sufficient silicon has been-'incorporated to make decarburization commercially feasible, and in general down to substantially 0.05 per cent.`

So 4vfar as carbon is concerned, naturally the lower the initial carbony the more readily and rapldly-canthe material be carried down tc a 'specific carbon content set up asa desired standf ard.' Inathel lighter gauges such as 29 gauge it is v not-necessary to have the carbon content lower than isno'rmally contained in open hearth heats, l in order toA accomplish successful decarburization withintheexceedingly brief times rindicated in our'several figures. For heavier'gauges, such as 24 gauge, the same time cycles can be achieved if theinitial carbon is in the neighborhood of 0.02 percent. Figs. `5 and 6 show the effector initial carbonA under varying conditions. It willA be understood, ofcourse, that-our method of` decarburization may be practiced upon materials previouslyl Y' partially decarburized by other methods. y. e ,A

*Wherever vwe have referred to an open anneal, we mean the carryingy of single or spaced multiple strips or single sheets of material through inch thick to as 'low' a value as was obtained with a threel minute annealof material oil-"the same analysis having' a gauge of 0.014- inch.

In Figs. 6 and 7," gauge appears as one of the variables and these diagrams will give'` the conditions to be expected over a range broad enough to take care of most commercial requirements.

The effect of the silicon content of materialsordinarily classified as' silicon steel yon the rate ofdecarburization seems to be vof much less importance. We have noted that when the per` centage of water vapor in hydrogen is less than four per cent by volume the higher grades 'of silicon steel.'siliconsteels containing the larger commercial quantities of silicon, decarburized at aslower rate, gauge'for gauge, than the lowerA Buton the other hand, if the' silicon grades. percentage of water vapor is increased to about an velongated heating chamber in which the entiresurface' of the material has free access to the surrounding lannealing atmosphere. This is. inv to" a so-'called box anneal in which f distinction atightly Wound coil or a large stack of relatively wide sheets is heated to and cooledl from the annealing temperature ,in such amanner that the annealing Vatmosphere does not have free and' uniform access to the entlre'surface of the eight per cent or more,'this eiect of silicon is not sov pronounced'. There are indications that as the silicon content increases the' optimum decarburizing temperaturev decreases somewhat.`

However, with steels V'containing Asubstantially over 4 percent silicon the rate of decarburization has been found to be so slow that the commer-l cial applications of the process become limited.

But' the presence of Vsome siliconis very important to this method of decarburization. While materials substantially or entirely free from silicon may be decarburized'I yet the presence of silicon even in very minor quantities, such as a small fraction of one percent, speeds up the Adematerial. fThe temperature is maintained within the preferredrange by any suitable heating means fincurrentuse in such furnaces, excepting,

of course, such heating means as would interfere with the maintenance of the necessary atmosphere.,r Electric heat and heat applied by means of 'radiant tubes are, of course, types of heating `means which permit great flexibility in the lcontrol of atmosphere.. Individual sheets may-,be Acarried, through the furnace on known heat-resisting driven conveyor systemsy orv the sheetslmay be stitched or otherwise fastened to-I gether so as to form theequivalent of a strip.

A strip material may be vvpulled throughthefurnace in ways current in the art. Although it' is theoretcallypossible todo sowe have not attempted toemploy recirculation in connection with the maintenance of the furnace atmosphere. We introduce vinto the furnace hydrogen or a suitable reducing atmospherecontinuously in suchvolume as to keep `oxidizing atmosphereout `of the furnace. As a consequence, some of the hydrogen or other reducing atmosphere escapes at the ends of the furnace where it is burned or carried out a stack.

By following this decarburizing procedure involving the use of Wet hydrogen, it is also coml mercially possible to decarburize silicon steel during a batch anneal in piles or coils in which the width of the material is not so great as kto prevent the effective access of the annealing atmosphere. -For example, we have found this method successful in decarburizing stacks of 4 inch wide pieces ofv a 0.014 inch thickness such as are used in transformer cores. Such a decarburizing anneal may be in addition to the final high temperature anneal, or it may be made a part of the regular high temperature anneal by providing the wet hydrogen when the charge is within the correct temperature range and maintaining the temperature of the charge within this range for an eiective llength of time.

This is preferably done during the heating period of the anneal which is then followed by the higher temperature portion of the anneal, which may be, for example, in an atmosphere of dry hydrogen at approximately 2200 degrees F.

The moisture content of the reducing atmosphere may be derived in several ways: lWe have vfollowed the practice of bubbling the'gas through a water bath at a proper temperature to ,give

the desired dew point.` We have also admittedcontrolled quantities of steam to the interior of the furnace when required to maintain a proper dew point. Dew point'tests are conducted from time to time and the atmosphere in the furnace is held at the required water vapor content, say between two and thirty-five percent by volume in ways which will be sufficiently understood by the skilled worker in the art. l

Now the provision of a brief open annealing operation which is effective in decarburization renders it possible for us to produce certain grades of silicon steel strip or sheet materialsY for magnetic uses without the necessity for any box annealing; and further in this connection, it will be observed that the decarburizing anneal can, if desired, be used as the. anneal or one of the anneals relied upon for producingthe desired magnetic properties. Y t

There are other cases where invorder to obtain the best magnetic properties it is necessary 'to produce a very low carbon material and it is further necessary that the material be box annealed. As has been mentioned, itis practically impossible to decarburize commercial 'widths of cold-rolled material during the iinal' box an'- nealing. In these cases an intermediate or 'nal decarburization in accordance with our teachings may be desirable in addition-to the regular final box anneal. Processes of reducing and treating silicon steel will Vary both with the analysis of the steel and with the final result desired, as will be readily understood by the skilled worker in the art. By way of example, a procedure which willproduce a silicon steel material characterized by substantially isotropic Vmagnetic properties will differ from a process producing a `silicon steel having extraordinarypermeability in the rolling direction and very much lower permeability in other directions. The various useful commercial properties in'silicon steel for mage netic uses may. however, be secured'by combining our new process of decarburization with com` binations of processing steps now used.` The advantages of these novel combinations will include in some cases lower production costs, in others the production of superior magnetic materials, in others superior physical properties, and

in still others the attainment of excellent magnetic properties which have hitherto'been 'impossible to produce. inwide sheets. We give below three exemplary processes falling within the scope of our invention.

In the first, process wefhot roll the silicon 4,; steel to the'most economical hot-rolled `thickness. Next we pickle it to remove the hot-mill scale and fit the material for cold rolling. Next we cold roll the material to within five to ten n per cent of the final gauge, depending upon the silicon content. Next we open anneal the material in wet hydrogen at 1400 to 1600 degrees F.

or thereabouts. 'I'his step constitutes not only a decarburizing treatment but is also the necessary preparatory to cold rolling; cold roll it to gauge and then open anneal it so that it is Vat 1500 degrees F. or thereabouts, in wet hydrogen for at least a portion iof the annealingcycle. The final annealing thus not only constitutes the carbon removal but alsoisthe final anneal for developy ing the desired properties.

In the production of a material characterized by extraordinary permeability in Itherolling directionthe following procedureis carried on (it being understood that the gauges lgiven are exemplary only and are intended to indicate proportional relationships) Hot roll the material to say 0.120 inch; box anneal the material for the sake yof uniformity in results in the'4 subsequent steps; cold roll to say 0.025 inch with such control of theftemperature as will result in an incipient twinned condition of ythe crystals; open anneal it so that it is at 1500 degrees F. or thereabouts in wet hydrogen foi-.at least a portion of the annealing cycle (wliichnot only decarburizes but constitutes the necessary annealing following the first cold rolling). so that the twinned condition of the crystals can grow ,by accretion; then cold roll to a final thickness. of say`0.012 inch with temperature control and then open anneal so that in the nal product the crystal orientation in the silicon steelispreponderantly of the twinderivative type.` This annealing again may be an annealing wet hydrogen, if desired.` A final box anneal may then be addedf or may replace this last open anneal. We havefound that the cold reduction at the first cold yrolling stage should be between substantially 60'per cent to substantially per cent, and at the second coldrolling stage, between substantially 50 per cent and substantially 85 per cent. Thev initial box anneal, if carried on in the presence of the hot mill scale will effect a partial decarburization of thev material. Another alternative in this process is to use an ordinary open anneal at the intermediate gaugev and decarburize in wet hydrogen only at the final gauge. It is to be understood that the specific gauges cited are only exemplary; andwhile they represent a preferred procedure, are not limitations ofthe process,lsince, for example, hot rolled starting Vthis stage such a materials varying in gauge from 0.07 to 0.15 inch have been effectively used.

This process as here brieily outlined is a modication, in accordance with our present invention,"of the processes set forth and claimed in Patent No. 2,158,065 to Cole and Davidson, issued May 16, 1939, and the copending application of Cole, Davidson and Carpenter, Serial No. 235,098, filed October 14, 1938, and the control referred to above is the control set forth in the said patent and application.

The twin-derivative type of crystal orientation mentioned in this process Vis one in which a preponderance of the crystals are aligned so that a (100)direction is substantially parallel to the rolling direction of the sheet anda (110) plane substantially parallel to the sheet surface.

The inclusion of our new step of decarburization in these processes has resulted in our being able consistently to produce material in Wide sheets which, in addition to high-induction permeability, have extremely low core loss. Heretofore it has been impossible consistently to produce wide sheets having extremely lowlcore loss because of thediiliculty of eliminating carbon from the centers of wide sheets during the nal box annealing in a hydrogenous atmosphere. The value of this new decarburization method to this particular process will at once be apparent.

In any of the above examples of cold-rolling processes involving wet hydrogen decarburization at intermediate or final gauges, under circumstances where it is desired to insure that the finished material will have a very low carbon content, such as 0.003 to 0.008` per cent, it may be commercially advantageous to introduce a decarburizing box anneal at 1200 to 1700 degrees F. for two to twenty-four hours of the unpickled, hot-rolled material prior to the cold rolling. In those'processes already having a box anneal at y decarburizing box anneal can be substituted. By a "decarburizing box annea we mean a box anneal in the presence of the hot-mill scale, or its equivalent.A

The wet hydrogen decarburizing process lcan effectively be introduced at other stages in the processing than those of thel above examples. For example it may be used following a final high-temperature anneal if the surface of the material is sufliciently clean. Any stage at which the gauge is suniciently thin so as not to require a non-commercial lengthy of time and at which the surface of the material is suiilciently clean will be satisfactory. The preferred conditiony is a cold-rolled surface or a surface cleaned by pickling or an equivalent surface. The presence of scale or reduced scale should be avoided.

While this decarburizingprocess has been described in its particular application to cold-rolled materiaLit is to be understood that'it is also applicable to hot-rolledv material. The same teachings as to gauge, carbon content, silicon content, moisture content, and surface condition are directly applicable. i h

Modiiications may be made in our invention without departing from the spirit of it. We have set forth hereinabove the varying factors covering both decarburization per se in accordance with our invention and procedures involving such a step.

which comprises open annealing said sheet or stripV at a temperature substantially within the range of 1350 to 1650 degrees,F., in an atmosphere predominantly 'of hydrogen and containto thirty-iive per cent anneal to reduce the carbon content of said silirolling itto gauge, and open annealing it so that Having thus described our invention, what we claim as new and desire tosecure by Letters Patent is:

1. A process of decarburizing silicon steel sheet or strip containing from 0.05% to 4% silicon characterized by high ing water vapor substantially within the range of two to thirty-five per cent.

2. A process of decarburizing silicon steel sheet oifstrip containing silicon between substantially 0.05% and substantially 4% and containing originally not -substantially less than 0.02 per cent carbon, and having a gauge not substantially greater than 0.025 inch, which comprises heating the sheet or strip at a temperature substantially within the range of 1350 to 1650 degrees F. in a non-oxidizing atmosphere predominantly of hydrogen and containing substantially four water lvapor in an open con steel to a value not greater than 0.01 per cent," but not exceeding 3,0 minutes in duration.

3. A process of producing silicon steel containing substantially 0.05% prises hot rolling the silicon steel to anv intermediate gauge, pickling it, cold rolling it to sheet gauge, and open annealing it so that for atleast a portion of the cycle it is a temperature sub- 'stantiallybetween 1400 and k1600 degrees F. in a reducing atmosphere containing Water vapor in an amount substantially between 4 and 35 per cent, whereby both to decarburize the steel and to developits magnetic characteristics.

4. A process of producing decarburized silicon steel containing substantially between 0.05% and hot rolling silicon pickling. it, cold.

4% silicon which comprises steel 'to an intermediate gauge,

for at least a portion ofthe cycle it is at a temperature substantially between 1400 and 1600 degrees F. in an atmosphere predominantly of hydrogen but containing water vapor in an amount substantially between four and thirty-five per cent, theinitial carbon content of said silicon steel being substantially within the range of 0.02 and 0.06 per cent, and said open annealing being carried on for a sufficient length of time to develop the magnetic characteristics of the material and to reduce the carbon contentof said silicon steel to a value not substantially greater than 0.01 percent, thefinal gauge of said material being not substantially greater than 0.025 inch-and the time vduration of said treatment lying substantially between two. and fourteen minutes. l

5.L A process of producing decarburized silicon steel containing from 0.05% to 4% silicon which comprises hot rollingit to an intermediate gauge, pickling it, cold rolling it to within vfive to ten per cent of final gauge, open annealing it at a temperature substantially between 1400 and 1600 degrees F. in a reducing atmosphere containing water vapor substantially between two and thirtyfive per centv whereby to decarburize the silicon steel, then cold rolling it to iinal gauge and iinal- 1y open annealing it at a temperature not substantiallyless than 1400 degrees F., whereby to develop its magnetic characteristics, the iinal gauge of said material being not substantially greater than 0.025 inch, the initial carbon content of said material lying substantially Within the range of 0.02 and 0.06 per cent and the final carbon content of said material being not substantially greater than 0.015 per cent.

6. A process of producing silicon steel containlng, substantially between 0.05% and 4% silicon, permeability in the rolling to 4% silicon which comorientation an incipient twinned condition of the crystals, open annealing the material so that` for at least a portion of the cycle it is at a temperature substantially between 1400 and 1600 degrees F. in an atmosphere predominantly of hydrogen but containing water vaporin an amount substantially between four and .thirtyve per cent, whereby bothto reduce the carbon content and to cause the twinned condition of the crystals to grow by accretion, again cold rolling the material with a reduction of substantially between 50 and 85 per cent while controlling the temperature as before, and nally open annealing the material whereby the crystal orientation in the finished material is predominantly of the twin-derivative type.

7. A process of producing silicon steel containing substantially 0.05% to 4% silicon, characterized by high permeability and low core loss in the rolling direction, and low carbon content, which comprises hot rolling the-material to a gauge substantially within the range of 0.07 and 0.15 inch, cold rolling the material to give it a reduction ofsubstantially between 60 and 85 per cent whilecontrolling the temperature `so as to produce in the metal in addition to cold-rolling orientation an incipient twinned condition of the crystals, open annealing the material so that at least for a portion of the cycle it is ata temperature substantially between 1400 and 1600-degrees F. in'a reducing atmosphere containing water vapor in an amount substantially between -four carbon content of said silicon steel being of the order of 0.02 nd 0.06 per cent and the final carbon content of said silicon steel being not substantially greater than.0.008 per cent.

8. A process of producing silicon steel containing substantially 0.05% to 4% silicon, characterized by high permeability and low core loss in the rolling direction, and low carbon content, which comprises hot rolling the material to a gauge substantially'within therange of 0.07 to 0.15 inch, cold rolling the material to give it a reduction of substantially between 60 and 85 per cent while controlling the temperature so as to produce in the metal in addition to cold-rolling orientation an incipient twinned condition of the crystals, open annealing the material so that for at least a portion of the cycle it is at a temperature substantially between-13.50 and. 1650 degrees F. in an atmosphere predominantly of hydrogen n' `but containing water` vapor in an amount substantially between twoand thirty-five percent, whereby both to reduce thecarbon contentandI tocause the twinned condition of the crystals to grow by accretion,` again cold rolling the material with ya reductionof substantially between 50 and 85 per cent while controlling the temperay ture asbefore, again open annealing the material at a temperature substantially between 135.0 and l 1650 degrees F. in an atmosphere :predominantly of hydrogen but ycontaining water vapor in `an amount substantially betweentwo` and thirtyfive `per cent',"l whereby to*` further vreduce .theV carbon content, and finally box-` annealing the,`

material predominantly in hydrogen, theilnal carbon content of said lsilicon steel being not substantially greater than 0.008 perl cent and the gaugeyand open annealingthe lsteel in an atmosphere of reducing gaslcontaining substantially two'to thirtyve' per cent water vapor at a temperature substantially between 1350 and 1650 F. so as to lower the-carbon content'still further. 11`. A process of mak-ingV low carbon ferrous materials which comprises producing a vferrous material containing. `at least 0.05 lto substantially 4 per cent silicon,reducing said` materialto a gauge not substantially vgreater than 0.025 `inch, and open annealing the reduced material ata temperaturesubstantially between 1350"y and l650 F. in'an atmosphere ofreducing gascontaining at least substantially two per cent water vapor so as to lowerthe carbon content thereof.

` l2. A process'of producing decarburized silicon steel containing substantially 0.05% to 4% silicon, including the steps of reducing silicon steel tov sheet-like form and annealing sa-idv steel to limpart desired magnetic properties thereto and whichl comprises subjecting the material to a y heat treatment withinthe range of. 1350 degrees inch, the duration vof said annealing treatment ,beingv from substantiallytwo to substantially fourteen minutes.

VICTOR W. CARPENTER. JOHN M. JACKSON. 

